My DD is 7 months and I want to get her to start using a "sippy" cup but the top is different to a bottle and she just doesn't want to give it a go. My DS took to it like a duck to water at 4 months but DD just gets frustrated with it and will scream until she gets her bottle. Any ideas? I've tried at different times of the day, different things in it (juice, water, formula) and even leaving it with her on her own to try it but nothing works.